1. Field of the Invention
This invention relates a molded plastic wheel and, in particular, to a hollow-form wheel with an independently formed rim for use on bicycles.
2. Brief Statement of The Prior Art
Plastic wheels for bicycles and other applications have been provided by a variety of molding techniques. A large number of prior patents disclose wheels which are made by injection molding, but which are not hollow-form. Instead, these wheels have solid ribs or spokes which extend between a central hub and outer rim. Examples of such patents are U.S. Pat. Nos. 4,508,392 and 4,793,659. Other attempts to provide a molded plastic wheel suitable for use on bicycles are described in U.S. Pat. Nos. 3,862,779 and 4,818,034. In these patents a hollow-form wheel is assembled from split, mirror image halves and the assembly is retained by suitable fasteners or studs. While this approach can provide a hollow form wheel, it compromises the strength of the wheel and requires substantial manual assembly.
Another attempt to provide a plastic bicycle wheel is disclosed in U.S. Pat. No. 4,844,552. This patent describes a spokeless wheel having a solid center which is formed by an assembly of annular diaphragms between a central hub and outer rim.
Molded plastic bicycle wheels have been marketed with limited success. These wheels are three-spoke plastic wheels which are made by applying multiple layers of resin impregnated graphite fiber onto a plastic foam or rubber mandrel that is placed in a mold and heated to cure the resin. The plastic foam mandrel remains in the wheel. The rubber mandrel is extracted from the hub and annulus areas of the wheel and a separate rim and a separate hub are bonded to the wheel by secondary bonding.
These procedures are very tedious and rely substantially on custom hand fabrication, and do not provide the precision and accuracy that is desirable for consistent performance in quality of the wheel.
In our prior U.S. Pat. No. 5,184,874 we disclose a one-piece, hollow form, injection-molded bicycle wheel in which the rim is integrally formed with the wheel. This wheel combines the best in strength and weight and ease of manufacturing. In some instances, however, it is desirable to provide a wheel of fiber reinforced plastic construction which has a separately formed rim, thereby permitting use of different materials for the rim, e.g., a metal rim, or a reinforced plastic of different composition than that of the remainder of the wheel.